The subject matter disclosed herein generally relates to air valves and, more particularly, to air valves of starters for aircraft engines.
Gas turbine engines used on modern aircraft are composed of a compressor, a combustion chamber, a turbine, and a main shaft connecting the turbine to the compressor. External air is compressed by the compressor and sent to the combustion chamber where an air-gas mixture combusts and provides thrust to the aircraft as it exits the engine. The combusted air-gas mixture also rotates the turbine as it exits the engine and the turbine rotates the compressor through the main shaft. At various times, the main shaft may need to be slowly rotated or motored to maintain thermal equilibrium throughout the engine.
In one example, after shutdown, the aircraft engine main shaft begins to bow due to thermal properties which can result in the rotor tips contacting the case wear path. This bowed condition is called the bowed rotor condition (BRC). The BRC creates the need for sub-idle motoring to cool the engine. When performing a manual start using a starter air valve manual override feature, the technicians cannot easily achieve the proper motoring speed and can cause an over speed condition which results in damage to the engine. A more efficient air valve design is desired.